Showing papers on "Microstructure published in 1971"
TL;DR: In this paper, the non-ohmic properties of ZnO ceramics with five additives of Bi2O3, CoO, MnO, Cr2O 3, and Sb 2O3 are studied in relation to sintering temperature, additive content, and temperature dependence.
Abstract: Nonohmic properties of ZnO ceramics with five additives of Bi2O3, CoO, MnO, Cr2O3, and Sb2O3 are studied in relation to sintering temperature, additive content, and temperature dependence. The observation of electron photomicrographs and X-ray microanalysis proves a ceramic microstructure such that ZnO and these five oxides form, at the grain boundaries, segregation layers which are responsible for the nonohmic properties. The electrical resistivity and dielectric constant of segregation layers are estimated to be 1013 ohm-cm, and 170, respectively by using a simple model. The electric field strength corresponding to the steep rise in the current is also estimated to be 104 V/cm by taking account of the concentration of applied voltage at the segregation layer. In view of these data and simple model, a possible explanation for nonohmic properties is discussed.
1,054 citations
TL;DR: Physical, electrical, and optical properties of selected compositions within the lead lanthanum zirconate-titanate (PLZT) system are presented, including chemically and thermally etched microstructures, examples of residual porosity defects, temperature dependence of remanent polarization and coercive field, lateral switching strains, and thermal expansion and optical transmission data as mentioned in this paper.
Abstract: Physical, electrical, and optical properties of selected compositions within the lead lanthanum zirconate-titanate (PLZT) system are presented, including chemically and thermally etched microstructures, examples of residual porosity defects, temperature dependence of remanent polarization and coercive field, lateral switching strains, and thermal expansion and optical transmission data. Optical-quality ceramics were produced by stringent raw material selection and improved ceramic processing and hot-pressing. Optimum results were obtained from starting oxides with higher purity (99.9%) and smaller particle size (<2 μm) than those used in previous investigations. These oxides were processed by methods developed to minimize segregation and promote chemical homogeneity and hot-pressed at temperatures (1050° to 1250°C) higher than those used previously to remove residual porosity.
191 citations
01 Dec 1971
TL;DR: In this article, the technique of heating rapidly through the Ac1 to Ac3 range, limiting the maximum temperature to the minimum required for complete austenitization and quenching immediately is discussed.
Abstract: The technique of austenitizing steel by heating rapidly through the Ac1 to Ac3 range, limiting the maximum temperature to the minimum required for complete austenitization and quenching immediately is discussed. Rapid austenitizing refines the austenite grain size if the initial microstructure is a fine aggregate, such as martensite or tempered martensite. Additional grain refinement usually results from two or more cycles and most steels hardenable by heat treatment become ultrafine grained and hence exhibit increased strength and toughness. Rapid austenitizing can also be applied, particularly to high-carbon steels, to develop a unique microstructure comprised of a uniform dispersion of very small carbide particles in an ultrafine grained martensitic matrix.
141 citations
TL;DR: Stress-strain curves have been obtained for the superplastically deformed Al-Cu eutectic tested in tension under constant true strain-rate conditions and it is shown that constant flow stress conditions do not obtain and that, after an initial transient, the flow stress is linearly related to natural tensile strain this article.
Abstract: Stress-strain curves have been obtained for the superplastically deformed Al-Cu eutectic tested in tension under constant true strain-rate conditions. It is shown that constant flow stress conditions do not obtain and that, after an initial transient, the flow stress is linearly related to natural tensile strain. Optical metallography has been employed to follow the variation of both inter-phase particle separation and α-Al grain size with strain and it is concluded that the observed strain hardening is due mainly to grain coarsening.
89 citations
TL;DR: In this paper, the pulse electrical strength of hot-pressed MgO containing 0.3 wt% LiF was measured and a simple recessed-electrode configuration eliminated corona effects.
Abstract: Pulse electrical strengths of hot-pressed MgO containing 0.3 wt% LiF were measured. Strengths as high as 5.9×108 V/in. were obtained on samples 99.8% of theoretical density with 1-to 3-μm grain size. An increase of either porosity or grain size resulted in a monotonic decrease in strength. Single-crystal strengths of 4.0×106 V/in. were obtained by polishing samples chemically. A simple recessed-electrode configuration eliminated corona effects.
82 citations
01 Nov 1971-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the influence of microstructure on the strength and fracture toughness of 18 Ni maraging steel was examined by X-ray and neutron diffraction and by optical and electron microscopy.
Abstract: The influence of microstructure on the strength and fracture toughness of 18 Ni (350) maraging steel was examined. Changes in microstructure were followed by X-ray and neutron diffraction and by optical and electron microscopy. These observations have been correlated with the fracture morphology established by scanning electron microscopy. Air cooling this alloy from the austenitizing temperature results in a dislocated martensite. During the initial stage of age hardening, molybdenum atoms tend to cluster (forming preprecipitates) and the cobalt assumes short range ordered positions. Subsequent aging results in Ni3Mo and σ-FeTi with overaging being associated with the formation of equilibrium reverted austenite and Fe2Mo. The fracture behavior is examined in terms of elementary dislocation precipitate interactions. It is suggested that the development of coplanar slip in the underaged conditions leads to its increased stress corrosion susceptibility and decreased fracture toughness. The optimum aged condition is then associated with cross-slip deformation. The fracture behavior of the overaged condition is a dynamic balance between a brittle matrix and the ductile (crack blunting) reverted austenite.
79 citations
01 Jan 1971
TL;DR: Fracture toughness of an α-Β titanium alloy heat treated to a constant yield strength has been found to depend upon the morphology of α produced or remaining after the initial solution treatment.
Abstract: Fracture toughness of anα-Β titanium alloy heat treated to a constant yield strength has been found to depend upon the morphology of α produced or remaining after the initial solution treatment. In equiaxed α structures, fracture toughness depends linearly upon the grain boundary area per unit volume,Sv, and is independent of equiaxed α particle size or spacing. In a grain boundary α structure fracture toughness depends both onSv and, within limits, linearly on the thickness of the α. Explanations are offered for the observed propagation of cracks at α-@#@ Β interfaces and for the observation that high fracture toughness can accompany low tensile ductility.
68 citations
01 Mar 1971
TL;DR: In this article, a study of Al-Zn-Mg alloys was undertaken to establish the specific combination of mechanical and thermal conditions which are necessary for stress-corrosion susceptibility to occur.
Abstract: This study of Al-Zn-Mg alloys was undertaken to establish the specific combination of mechanical and thermal conditions which is necessary for stress-corrosion susceptibility to occur in these alloys. The work included a study by electron transmission microscopy of the microstructure of this alloy system. A new mechanism is proposed to account for the observations made. It suggests that the high corrosion potential at grain boundaries in stress-corrosion susceptibile Al-Zn-Mg alloys is due to segregation of zinc and magnesium. By taking precautions to reduce this segregation, the stress-corrosion life can be increased.
56 citations
TL;DR: In this article, the same consolidation parameters and intimate mixing of residual concentrations of highly active fine-particulate rare-earth oxides to act as grain growth inhibitors were used to obtain nearly theoretically dense bodies with a uniform microstructure and 1 to 1.5 μm grain size.
Abstract: Polycrystalline BaTiO3 prepared from alkoxy-derived high-purity submicron powders was studied. Highly dense bodies with uniform grain size were obtained typically by uniaxial cold-pressing at 3000 psi and isostatic pressing at 30,000 psi followed by sintering at 1300° to 1350°C in air for 0.5 to 1 h. Using the same consolidation parameters and intimate mixing of residual concentrations of highly active fine-particulate rare-earth oxides to act as grain-growth inhibitors, nearly theoretically dense bodies with a uniform microstructure and 1 to 1.5 μm grain size were obtained. Typical microstructures with well-defined 90° and 180° domain patterns characteristic of BaTiO3: were observed. Also, an example of a checkerboard pattern resulting from a 〈111〉 ingrown twin plane in the structure which is independent of the Curie temperature was found. Electrical measurements on the undoped material indicated room-temperature dielectric constant and tan δ values of 5000±500 and 4×10−3, respectively. Very high k values and dissipation factors were observed with the La2O3- and Nd2O3-doped samples.
51 citations
38 citations
TL;DR: In this article, the effects of nickel coatings on the room-temperature fracture strength and microstructure of individual carbon fibres have been investigated, and the reduction in strength was not related to fibre recrystallisation, but appeared to be controlled by the formation of a carbon-nickel interface, with an energy for adhesion of approximately 110 kcal mole−1.
Abstract: The effects of evaporated pure nickel coatings on the room-temperature fracture strength and microstructure of individual carbon fibres have been investigated. The fracture strength of a nickel-coated fibre was not affected by anneals in a 10−6 torr vacuum below 1000°C. However, after higher temperature anneals a reduction in strength was noted, the magnitude of which was time-dependent, but almost independent of the thickness of the coating. The reduction in strength was not related to fibre recrystallisation, but appeared to be controlled by the formation of a carbon-nickel interface, with an energy for adhesion of approximately 110 kcal mole−1.
01 Dec 1971
TL;DR: In this paper, room temperature tensile tests have shown that composites of an Al-13 wt pct Si alloy and Thornel 50 graphite fibers have strengths greater than a theoretical value that was calculated on the basis of the law of mixtures.
Abstract: Room temperature uniaxial tensile tests have shown that composites of an Al-13 wt pct Si alloy and Thornel 50 graphite fibers have strengths greater than a theoretical value that was calculated on the basis of the law of mixtures. At 28 vol pct fibers, the average uniaxial tensile strength was found to be 106,000 psi, and several values between 130,000 and 144,000 psi were obtained. The modes of deformation and failure in the composites have been studied by the microexamination of polished surfaces and fractures of tested specimens. The reasons for the high strengths and the unusual modes of fracture that were observed cannot be explained on the basis of the presented data. Specimens of the composite have been thermally cycled between −193° and +20°C twenty times and others between −193° and +500°C twenty times. Tensile tests and microexamination of these thermally cycled specimens show that thermal cycling does not degrade the tensile properties of the composites or change their microstructure.
TL;DR: The grain growth and densification rates of Mn-Zn ferrites during sintering are closely linked to the characteristics of the calcined and milled powders used as mentioned in this paper.
Abstract: The grain growth and densification rates of Mn-Zn ferrites during sintering are closely linked to the characteristics of the calcined and milled powders used. Long milling times enlarge powder particle size distributions and tend to promote discontinuous grain growth during sintering. For fixed sintering conditions, an optimum milling time, which corresponds to minimal eddy current and hysteresis losses, exists. The electrical properties of overmilled powders deteriorate greatly because duplex structure occurs. Theoretical analysis of the probability of discontinuous grain growth occurring during sintering in relation to powder particle size distribution agrees with the experimental results.
TL;DR: In this article, the deformation, yield and brittle fracture properties of an 84% trans-polychloroprene (Neoprene W) were determined at −180°C for samples prepared with a range of microstructures (including amorphous, row-nucleated and spherulitic morphologies).
Abstract: The deformation, yield and brittle fracture properties of an 84% trans-polychloroprene (Neoprene W) were determined at −180°C for samples prepared with a range of microstructures (including amorphous, row-nucleated and spherulitic morphologies) and a range of pre-orientations from 0 to 300%. Pre-orientation was carried out at room temperature and crystallisation, where required, at −5°C. The degree of crystallinity was low, in the region of 18%, and the crystalline morphology was monitored by thin film electron microscopy and by wide angle X-ray analysis.
TL;DR: In this article, aluminum films with grain boundaries staggered throughout the film thickness, and hence with nonoverlapping sites for electromigration-induced failure, were prepared by vacuum deposition in layered or extremely fine-grained form.
Abstract: Aluminum films with grain boundaries staggered throughout the film thickness, and hence with nonoverlapping sites for electromigration‐induced failure, were prepared by vacuum deposition in layered or extremely fine‐grained form. Mean lifetimes before the occurrence of electrical opens were an order of magnitude larger than those for control films having non‐redundant grain structure. Heat‐treatment effects which reduced lifetimes to values comparable to control lifetimes were interpreted in terms of either a lifetime minimum for grain size ∼ 0.6 μ or disruption of the layered structure.
TL;DR: In this article, an attempt is made to relate the unusual irradiation behavior of Poco graphite to its microstructure, showing that the graphites behave isotropically under irradiation and show improved dimensional stability over conventional nuclear graphites.
TL;DR: In this article, the authors found that wear loss is dominated by viscoelastic properties of tire treads and the combined effect of the cis, trans, vinyl, and styrene content.
Abstract: 1. Car, wheel position, driver, inflation pressure, and shoulder drop have a statistically significant effect upon wear loss and need to bo taken into consideration before material factors affecting wear can be studied. 2. Variations in macrostructure of the polymers are not found to have a significant effect on wear as compared to microstructure variations. 3. At least two material factors control wear loss of tire treads. 4. When polymers are tested near their glass transition temperature (within 80° C), wear loss is dominated by viscoelastic properties. Viscoelastic properties can be related to wear loss through Tg or the combined effect of the cis, trans, vinyl, and styrene content. 5. At higher test temperatures (over 100° C above Tg) wear loss is dominated by a material factor that has a positive correlation with temperature. This is particularly noticeable when treads are worn under mild conditions. However, there is evidence that this wear factor is present at the testing nearer to Tg but...
01 Nov 1971
TL;DR: In this paper, the importance of grain boundary precipitate spacing and grain boundary microstructure in stress corrosion susceptibility was investigated in a chloride ion environment over a 0.7 -3.5 pH range.
Abstract: : Matrix and grain boundary features were systematically varied, using appropriate heat treatment, to evaluate their significance in changing the mechanical and stress corrosion properties of 7075 aluminum alloy. Maximum strength is associated with a Guinier-Preston zone matrix. The precipitate-free-zone adjacent to high angle grain boundaries was found to have only a slight effect on yield and tensile strength and a greater influence on hardness. Stress corrosion susceptibility was studied in a chloride ion environment over a 0.7 - 3.5 pH range. Differences in pH-dependent susceptibility associated exclusively with grain boundary structure for material of highest strength were observed. Grain boundary precipitate spacing (inversely related to precipitate density) was found to be of primary importance to susceptibility. The relative importance of crack initiation to the over-all stress corrosion process was also found to be dependent on grain boundary microstructure. These results indicate that improved properties for Al-Mg-Zn type alloys can be attained by a desirable combination of matrix and grain boundary structure. (Author)
01 Jan 1971
TL;DR: In this article, electron microscopy of thin PbTe films was performed on the cleavage face of NaCl with substrate temperatures of 100 and 300 °C and deposition rates of approximately 100 and 1000 A/min, respectively.
Abstract: Epitaxial thin films of PbTe have been prepared by vacuum evaporation onto the (001) cleavage face of NaCl with substrate temperatures of 100 and 300 °C and deposition rates of approximately 100 and 1000 A/min, respectively. Electron diffraction showed the films to be strongly oriented with the (001) planes of the deposit parallel to the substrate. Transmission electron microscopy of thinner films, ≈ 0.2μ thick, showed no significant variation in microstructure with changes in substrate temperature and deposition rate. Such films showed a high density of dislocations, ≈ 5×1010/cm2, the majority of which ran normal to the plane of the film. Many were arranged in low‐angle grain boundaries, the most prominent microstructural feature of the films. These exhibited rotations up to about 2° and the average boundary spacing for these thin samples was estimated at 2000 A. Surface replication of a number of films grown with comparable conditions but varying thicknesses show features that could be indicative of int...
01 Jan 1971
TL;DR: In this paper, microstructural features of the oxide scales formed under these conditions are studied as a function of temperature and reaction time, and techniques used to characterize the oxide products include x-ray diffraction, scanning electron microscopy and electronprobe microanalysis.
Abstract: Both ZrB2 and ZrB2 + 20 v/o SiC have been oxidized in oxygen over the range 900° to 1500°C. The microstructural features of the oxide scales formed under these conditions are studied as a function of temperature and reaction time. Techniques used to characterize the oxide products include x-ray diffraction, scanning electron microscopy and electronprobe microanalysis. A glassy B2O3 is one of the oxidation products at temperatures below 1100°C, resulting in protective behavior. At higher temperatures the formation of an SiO2-base glass imparts additional protection to ZrB2 + 20 v/o Sic.
TL;DR: In this paper, the variation of the postirradiation creep-rupture properties with irradiation temperature has been evaluated for air- and vacuum-melted Hastelloy-N.
Abstract: The variation of the postirradiation creep-rupture properties with irradiation temperature has been evaluated for air- and vacuum-melted Hastelloy-N.The air-melted material was high in silicon and ...
01 Feb 1971
Journal Article•
Patent•
24 Mar 1971
TL;DR: In this paper, hot isostatic compacting of titanium or titanium base alloy powder to a product having controlled interstitials and microstructure and possessing outstanding end properties, low porosity and high density and one which does not require subsequent forging.
Abstract: Hot isostatic compacting of titanium or titanium-base alloy powder to a product having controlled interstitials and microstructure and possessing outstanding end properties, low porosity and high density and one which does not require subsequent forging.
Patent•
21 Sep 1971
TL;DR: In this article, a martensitic or bainitic alloys containing up to about 25 percent Ni, 15 percent Mn, 1.2 percent C, 0.5 percent N are cooled to remove the principal nucleating effect of the prior austenite boundaries and other microstructural interfaces, so that when subsequently heated into the multiphase region, recrystallization occurs by random nucleation of extremely fine austenitic crystals thoughout the material.
Abstract: Ferrous alloys containing up to about 25 percent Ni, 15 percent Mn, 1.2 percent C, 0.5 percent N are cooled to form a martensitic or bainitic structure. The material is then worked to an extent sufficient to remove the principal nucleating effect of the prior austenite boundaries and other microstructural interfaces, so that when subsequently heated into the multiphase region, recrystallization occurs by random nucleation of extremely fine austenite crystals thoughout the material. Exceptionally fine equiaxed grains in the micron and submicron range are achieved, thereby providing unique combinations of both increased strength along with increased ductility and increased notch toughness.
Patent•
22 Jul 1971TL;DR: In this paper, columnar grain structure and improved high temperature, high mechanical strength properties are provided in a metal article by solid state method by forming the article in a manner which places the metal microstructure in a condition of dislocation density which results in the metal macrostructure undergoing relatively rapid transformation to relatively large grains when heated in the range of about 50 to less than 100 percent of the metal incipient melting temperature in degrees Rankine.
Abstract: A columnar grain structure and improved high temperature, high mechanical strength properties are provided in a metal article by solid state method. First the article is formed in a manner which places the metal microstructure in a condition of dislocation density which results in the metal microstructure undergoing relatively rapid transformation to relatively large grains when heated in the range of about 50 to less than 100 percent of the metal incipient melting temperature in degrees Rankine. Then the article so preconditioned is progressively and selectively heated in that temperature range but below the incipient melting temperature of the metal. This is accomplished by heating the article in a narrow zone. Such zone traverses the article, as a result of relative movement between the article and the source of heat energy, from the cooler portion and in the direction desired for growth of the principle axis of the columnar grains, with the zone having a thermal gradient of at least about 500 DEG F/in. A preferred form of a processed wrought article is characterized by grains of at least about 2000 microns in diameter and a length to diameter ratio of at least about 10.